In a normal manner, with reference to FIG. 1, a fuel injector 1 comprises a piezoelectric actuator 2 which acts on a valve means in order to open or close the injector 1, allowing or stopping the injection of fuel C into a combustion chamber of the engine of the vehicle, respectively. In known manner, the vehicle comprises an on-board engine control unit (not illustrated) in order to activate the piezoelectric actuator 2 and to control the injection.
As is known, a piezoelectric actuator 2 is principally composed of a stack of ceramic members which define a predetermined length, which has the property of causing this length to be modified under the action of an electric field and conversely producing an electric field under the action of mechanical stress.
In a fuel injector 1, a piezoelectric actuator 2 is arranged between a stop of the injector and a valve means. In practice and in summarized manner, when an electric charge is applied to the piezoelectric actuator 2 using an electric voltage, the length thereof increases and opens the valve means of the injector 1 which thereby releases fuel C under pressure into the combustion chamber.
More specifically, still with reference to FIG. 1, in the case of an injection system comprising a common high-pressure injection rail, the valve means comprises a mushroom-like closure member 3 which is actuated directly by the piezoelectric actuator 2, and a needle 4 which is actuated by its contact with the high pressure in the injector, which is made possible by the movement of the mushroom-like closure member 3 toward the opening position thereof under the action of the piezoelectric actuator 2. The needle 4 of the injector 1 is suitable for being moved between a closure position and an opening position, referred to as an injection position. The injector is a “servo valve” injector comprising a valve means which is configured to place a volume of high-pressure fuel of the injection rail in connection with a low-pressure volume of the fuel tank. In other words, the piezoelectric actuator 2 allows the needle 4 to be caused to move in an indirect manner.
In practice, the piezoelectric actuator 2 moves the mushroom-like closure member 3 which allows, when it is opened, the high pressure which is from the injection rail and the low pressure of the return circuit of the fuel to the tank to be placed in connection, which modifies the force equilibrium at the terminals of the needle 4 of the injector 1, allowing an upward movement thereof. As a result of this upward movement, the needle 4 releases the openings of the nozzle 5 of the injector 1, which allows the injection of the fuel C into the combustion chamber to be brought about under the action of the high pressure of the rail.
In the rest state, that is to say, in a closure position of the valve means (with the mushroom-like closure member 3 and needle 4 closed), there is a play J between the piezoelectric actuator 2 and the valve means, more specifically between the piezoelectric actuator 2 and the mushroom-like closure member 3, in order to ensure the closure of that valve means and to prevent uncontrolled leaks of fuel toward the combustion chamber. This play J will be referred to in the remainder of the present text either using the complete term or using a shortened form “actuator play”. This actuator play J is normally a few micrometres.
Over time, as a result of wear, the value of the actuator play J may develop which disrupts the operation of the injector 1. This is because the quantity of fuel C supplied by the injector 1 is no longer sufficient, which may bring about malfunctions of the engine of the vehicle.
An ideal solution would be to measure directly the effective value of the actuator play J. However, that requires, on the one hand, that the injector 1 be disassembled from the vehicle and, on the other hand, very specific tooling in order to allow the measurement of the actuator play J. In practice, therefore, the actuator play J is only rarely measured.
An ideal solution would be to integrate a distance sensor in order to measure the actuator play J. Such a solution cannot be implemented given the compact nature of the injector 1 and the order of magnitude of the actuator play J.
Furthermore, in order to allow an effective injection of fuel, it has been proposed to control the injector 1 in order to compensate for the development of the actuator play J, as set out by the patent application US2013066538A1. In the remainder of the present text, this method is referred to as the “compensation method”.
According to the compensation method, the injector 1 is controlled in order to simulate a preceding injection step so as to determine a charge time TMES which is measured between the actuation time of the piezoelectric actuator 2 and the time from which the mushroom-like closure member 3 begins to move. This charge time TMES corresponds to the extension duration of the piezoelectric actuator 2 until it compensates for the actuator play J. In order to compensate for the development of the actuator play J, it is known to increase the injection energy in accordance with the predetermined charge time TMES. In this manner, the quantity of fuel supplied by the injector 1 is correct in spite of the presence of the actuator play J.
However, such a compensation method does not allow an estimate of the value of the actuator play J in order to determine whether it is tending to deteriorate. Thus, in the event of malfunction of the vehicle, a mechanic may diagnose that the actuator play of the injectors 1 is too high and replace them. However, this diagnosis is not based on any objective piece of data and has limited reliability. In practice, it appears that a large number of injectors 1 are replaced needlessly, which increases the maintenance costs of a vehicle and constitutes a disadvantage. Furthermore, in the event of failure of an injector, it is necessary to immobilize the vehicle, which places the user thereof at a disadvantage.
There is a need to monitor in a reliable manner a fuel injector in order to anticipate a malfunction before it becomes effective and places the user at a disadvantage.